Seasonal Occurrences of Larval, Juvenile and Young Fishes in the Floodplain of a Mekong Tributary, Lao P.D.R.

Abstract

We studied the seasonal occurrences of larval and juvenile fishes in floodplain habitats of a tributary of the Mekong River in Lao P.D.R., by seining the center of a floodplain lake, its inundated area, its shoreline, and the littoral zone of the river, from March (the end of the dry season) to August (the middle of the wet season) 2006. We collected 2,084 individual larval and juvenile fishes representing seven orders, 13 families, and at least 32 species. Twentynine species occurred in the floodplain. Of these, 28 species occurred in the temporal waters (inundated area and shoreline). Nine species occurred in the littoral zone of the river. The mean catch per unit effort (CPUE) of juveniles in the temporal water was 7.3 to 14.5 times that of the permanent water (the center of a floodplain lake) in the middle of the wet season. Many larval and juvenile fishes were observed in the early part and the middle of the wet season. The dominant species changed dramatically among seasons. The temporary waters of the floodplain were considered important nursery grounds for both floodplain and riverine fishes. The littoral zone of the river was used by a limited number of species in the early wet season; however, after the water level fell it seemed to become an important nursery ground for species whose juveniles grew in the floodplain. The habitat use patterns and spawning triggers for the nine dominant species and an additional four species were discussed.